First phase of adding a special '*' bandwidth to the top file
This value can be specified in place of an integer bandwidth. When this is done, assign will map the virtual link to *any* physical link of the right type, regardless of bandwidth. However, it will adjust the bandwidth used for trunk calculations, etc, based on the bandwidth of the interfaces selected, so that this doesn't cause us to overuse interswitch links. For the time being, it is not legal to use this option with trivial links or emulated (multiplexed) links, since it's not at all clear what this would mean. This commit contains only the data structure and parser changes; the actual implementation will come soon.